Site-Specific and Size-Dependent Bonding of Compositionally Precise Gold-Thiolate Nanoparticles from X-ray Spectroscopy

Understanding the site-specific and size-dependent structure and bonding properties of gold-thiolate nanoparticles is one of the most fundamental questions in nanoscience. The recent synthesis of compositionally precise Au-m(SR)(n) nanoparticles offers a promising opportunity to explicitly elucidate the structure-property correlation of nanomaterials from site-specific and size-dependent perspectives. Herein we report an X-ray absorption (gold L-3-, sulfur K- and K-3,K-2-edge) and photoemission (gold 4f, sulfur 2p, and valence band) study of compositionally precise Au-m(SR)(n) nanoparticles. An X-ray spectroscopy approach to deduce the atomic structure of Au-144(SR)(60) is first demonstrated. In conjunction with ab initio calculations a high-percision atomic-site-specific illustration of the bonding in Au-144(SR)(60) is achieved. By comparing size-varied samples [Au-144(SR)(60), Au-38(SR)(24), and Au-25(SR)(18)], the size dependent nature of bonding in gold-thiolate nanoparticles is revealed from both the sulfur and gold perspective.